Acoustic computer communication techniques have been developed as an alternative to IR and RF wireless communication. Unlike IR and RF, acoustics does not suffer from such unexpected environmental conditions as sunlight, rain, metal objects, and can be “hidden” from people if its frequency is higher than 20 kHz. Indeed, IR usually requires direct visibility and is hampered by sunlight or bright interior light. Also, IR has such unexpected features as propagation through materials (that are not transparent in visible light) and reflection from various materials. RF, in turn, suffers from interference problems and can be blocked by metallic objects.
Various advantageous features of the acoustic-based communication, as well as examples for protocols for acoustic transmission, are disclosed in the following article: “Things that talk: Using sound for device-to-device and device-to-human communication”, V. Gerasimov and W. Bender, IBM Systems Journal, Vol. 39, Nos 384, 2000, pp. 530-546. This article suggests using ultrasound for device-to-device communication and using audible signals when devices communicate to human listeners.
Methods for communicating with an electronic device utilizing acoustic transmission below 100 kHz are disclosed in WO 00/21020 and WO 00/21203. WO 00/21020 describes a smart card comprising a memory for storing information; at least one transmitting or receiving antenna (which may be acoustic antenna); and a low frequency circuit, for handling information associated with said antenna and said memory, which information is modulated at a modulation frequency of between 5 kHz and 100 kHz. WO 00/21203 describes a method of communicating with an electronic device via acoustic signals with the frequency below 50 kHz. This technique consists of providing a computer having an audible sound receiving and generating sub-system including a microphone; transmitting from a source at least one ultrasonic acoustic signal, encoded with information to the computer; and receiving said at least one signal by said microphone, to be detected by said computer.